A combo box is a list of items that the user can select from. Like a list box, a
combo box is usually made of a list of strings. Unlike a list box, a combo box saves space by using just as much room as
a text box control. To show that it is holding a list, a combo box displays a
down-pointing arrow on the right side of its text box. In the following
screenshot, the Font Effects property page of the Character dialog box of
OpenOffice.org presents the Underlining,
the Color, the Effects, the Strikethrough, the Relief, and the Font Color combo
boxes:

Because a combo box does not (permanently) display its list like a list box, to
show its content, the user can click the arrow button. Here is an example:

Creating a Combo Box

To support combo boxes, the .NET Framework provides a class named ComboBox.
At design time, to add a combo box to your application, from the Common
Controls section of the Toolbox, you can click the ComboBox button
and click the form or a container. Like ListBox, the ComboBox
class is derived from the ListControl class. Therefore, to
programmatically create a combo box, declare a variable of type ComboBox,
allocate its memory with the new operator and add it to the Controls
collection of its container. Here is an example: